Separation process for alkylated aromatic compounds and olefinic oligomerizaton products



Aprll 8, 1969 J. E. GANTT 3,437,708

SEPARATION PROCESS FOR ALKYLATED AROMATIC COMPOUNDS AND OLEFINICOLIGOMERIZATION PRODUCTS Filed Sept. 12, 1967 w MEQ to t I\ n an 'L q mw a l r j //VV/V7'0R-- James E. Gan" A TTORNEYS United States Patent QUS. Cl. 260671 13 Claims ABSTRACT OF THE DISCLQSURE Process forseparating a reaction zone efiluent containing at least three componentswhich comprises passing the eflluent to a flash zone, passing theresulting flash vapor to a partial condensing zone, recycling theresulting vapor component from the partial condensing zone to thereaction zone, passing the resulting flash zone liquid and the resultingpartial condensing zone liquid to a fractionation zone, separating theliquids therein to provide at least a first liquid component and asecond liquid component, recycling a part of the first liquid componentto the reaction zone, and recovering the second liquid component. Theprocess is particularly applicable to the recovery of alkylated aromaticcompounds such as cumene and to recovery of oligomerized products suchas propylene-trimer.

Field of invention The present invention relates to a separation processfor recovery of product from a reaction zone eflluent containing atleast three components. The present invention particularly relates tothe separation of the effluent from an alkylation reaction zone toprovide a diluent stream for return to the reaction zone, a reactantstream for return to the reaction zone, and a product stream ofalkylated aromatic compound. The inventive process also relates to theseparation of the effluent from an oligomerization reaction zone toprovide a diluent stream for return to the reaction zone, a stream ofpartially-oligomerized product for return to the reaction zone, and aproduct stream of oligomerized product. Most particularly the presentinvention relates to a method of separation which results in an improvedprocess for alkylation of benzene with a propylene-propane mixture, forthe alkylation of benzene with an ethylene-ethane mixture, for theoligomerization of propylene in a propylene-propane mixture, and for theco-oligomerization of propylene and butene in a reactive mixturecontaining propane and butane.

The present invention finds one broad application in the production ofalkylated aromatic hydrocarbons for use in subsequent chemicalsynthesis. The present invention particularly finds application in theproduction of isopropylbenzene, or cumene, which is utilized in thesynthesis of phenol, acetone, alpha-methylstyrene, and acetophenone.These cumene-derived chemicals are intermediates in the synthesis ofresins for plastics and nylon. A further application of the inventiveprocess is in the synthesis of ethylbenzene. Virtually all of theethylbenzene commercially produced is dehydrogenated to styrene monomer,although small quantities are used as solvents and as intermediates inthe synthesis of other Patented Apr. 8, 1969 chemicals.Ethylbenzene-derived styrene (finds utility in the synthesis ofpolyester resins, polystyrene and other plastics, as Well as in thesynthesis of styrene-butadiene rubber and in the formulation of coatingsincluding latex paints.

Application of the inventive process may also be found in the alkylationof substituted aromatics such as phenol, which when alkylated withisobutylenes forms O-tertiarybutylphenol which is an intermediate in thesynthesis of other chemicals, and forms p-tertiarybutylphenol which isused to modify phenolformaldehyde resins. A further application of theinventive process upon substituted aro matic hydrocarbons may be foundin the alkylation of para-hydroxyanisole with tertiary butyl alcohol orisobutylene to form butylated hydroxyanisole which finds utility as anantioxidant in the preservation of foods.

The present invention finds additional application in theobligomerization of olefin-acting compounds. Oligomerization ofpropylene may be undertaken to produce commercial fractions ofpropylene-trimer and propylenetetramer, Within the scope of theinventive process. Trimer finds utility in the synthesis of nonyl-phenoldetergents and in the synthesis of decyl alcohols by the Oxo Process.Tetramer is also used in the synthesis of detergents. The inventiveprocess also finds application in the synthesis of commercial fractionsof heptene which are produced by the co-oligomerization of propylene andbutenes in a reaction mixture comprising propylene, propane, butene, andbutane. Heptene is utilized in the synthesis of octyl alcohols by the0x0 Process. (It is to be noted that oligomerization of olefinhydrocarbons is more commonly referred to as polymerization of olefinsin the petroleum refining industry.)

Description of the prior art As indicated above, the present inventionparticularly relates to the recovery of isopropylbenzene, or cumene froman alkylation reaction eflluent. In the commercial manufacture of cumeneit is the art to charge benzene and propylene into a reactor containinga solid phosphoric acid catalyst.

Because it is desired to minimize the dialkylation of benzene whichproduces di-isopropylbenzene by-product, it is the art to have a molardeficiency of propylene in the reaction zone and normally thisdeficiency is provided by maintaining the ratio of benzene to propyleneat about 8: 1. The resulting alkylation effluent Which leaves thereaction zone will therefore contain about seven moles of unreactedbenzene per mole of product cumene, and the excess benzene must beseparated from the efiluent and recycled to the reaction zone inconjunction with the fresh benzene feed which is charged to the process.

The propylene reactant which is typically charged to the process willcontain unreactive diluent comprising propane with traces of ethane andbutane. When the propylene feed is derived from a Pyrolysis Plant thesediluents will normally be less than 10 mole percent, While a propylenefeed derived from the gas recovery unit of a Fluid Catalytic CrackingPlant will often contain as much as 35 to 40 mole percent of unreactivediluents. In addition to the unreactive propane diluent which isinherent in the propylene feed, it is typically the art to introduceadditional propane diluent into the reaction zone to provide a thermalquench for the exothermic alkylation reaction in order that the catalysttemperature may be controlled at the desired level. This propane quenchmay be introduced into the reactor at elevated temperature with thepropylene-propane fresh feed, or it may be introduced at elevatedtemperature or at ambient temperature into the reaction zone at severalintermediate quench points. between several catalyst beds. Thealkylation effluent which leaves the typical reaction zone thereforcontains a considerable amount of propane diluent. This diluent must beseparated from the efiluent in order that a portion may be recycled tothe reaction zone and in order that a quantity may be withdrawn from theprocess. The quantity withdrawn is equivalent to the quantity which isbeing introduced into the process in the propylene-propane feed, and itmust be withdrawn from the process in order to avoid accumulation ofunreactive diluents in the process unit.

It is the art in the manufacture of cumene to charge the alkylationefiluent to a fractionation train comprising a depropanizer column, abenzene column, and a cumene column. The effiuent enters thedepropanizer wherein the propane diluent is removed overhead to providethe propane recycle stream for return to the reaction zone and a netpropane product stream which is normally withdrawn to the fuel gassystem or sent to produce storage as liquefied petroleum gas (LPG). Thebottoms liquid from the depropanizer passes into the benzene columnwhich produces a benzene overhead stream. Part of the benzene producedprovides the required recycle to the reaction zone and a second part iswithdrawn from the process in order to avoid the accumulation ofnonaromatic contaminants which enter the process as trace constituentsin the benzene feed. The benzene column bottoms pass to a cumene columnwhich produces an overhead comprising high purity cumene product and abottoms by-product comprising polyalkylated benzene.

The inventive separation process is equally applicable in theoligomerization of an olefin-acting compound in the presence of anunreactive diluent wherein a desired oligomerized product is producedand partially-oligomerized product must be separated therefrom. Forexample, in the production of propylene-tetramer a typicalpropylenepropane feed is oligomerized over a solid phosphoric acidcatalyst to produce a reactor effluent usually comprising propane,propylene-dimer, propylene-trimer, propylene tetramer andpropylene-pentamer. It is therefore necessary to depropanize the reactorefiluent in order to provide a recycle diluent propane stream forcatalyst temperature control and to recycle the propylene-dimer andpropylene-trimer to the reaction zone for further oligomerization withpropylene to produce additional product propylene-tetramer. It is wellknown to those skilled in the art, that the required separation of thereactor efiiuent is accomplished by passing the effluent into a seriesof fractionating columns comprising a depropanizer column, a column forobtaining the desired recycle fraction of partially-oligomerizedproduct, and a column for recovery of the desired oligomerized product.

The inventive process is similarly applicable to the separation of thereactor efiluent resulting from the synthesis of heptene byco-oligomerization of propylene and butenes. The unreactive diluentwhich must be recycled to the reactor for temperature control normallycomprises a mixture of propane and butane. Because the olefinic feedcontains propylene, butenes, and possible traces of other olefins, thereactor effluent will contain hexenes, heptenes, octenes, and heavieroligomerization products. It is the art to recover heptenes and octenesas the product fraction and to recycle hexenes and lighter olefins foradditional oligomerization. It is well known to those skilled in the artthat this separation of the oligomerization reactor efiluent isaccomplished in a series of fractionating columns which are operated ina conventional manner.

Summary of the invention It is an object of the present invention toprovide a method for the separation of a process stream containing atleast three components. It is a further object of the present inventionto provide a process for the separation of a reaction zone effluent. Itis a particular object of the present invention to provide a separationprocess for the recovery of alkylated aromatic compounds from theefiiuent of an alkylation reaction zone and for the recovery ofoligomerized products from the efiiuent of an oligomerization reactionzone. It is a specific object of this invention to produce ethylbenzene,cumene, heptene, propylene-trimer, and propylene-tetramer in a moreeconomical and facile manner.

These and other objectives will be readily ascertained from thefollowing description and the attached drawing which is a simplifiedflow diagram setting forth one specific embodiment of the invention.

In accordance with these objectives, a broad embodiment of thisinvention may be characterized as a process for separating a reactionzone eflluent containing at least three components which comprisespassing the efiluent from a reaction zone into a flash zone maintainedunder separation conditions; withdrawing from the flash zone a. firstfraction comprising a first component and a first part of a secondcomponent and a second fraction comprising a second part of the secondcomponent and a third component; passing the first fraction into apartial condensing zone maintained under separation conditions;withdrawing from the partial condensing zone a third fraction comprisingthe first component and a second fraction comprising the first part ofthe second component; passing the second fraction and the fourthfraction into a separation zone under conditions sufficient to provideat least a lfifth fraction comprising the second component and a sixthfraction comprising the third component in high concentration; passingthe third fraction and at least a part of the fifth fraction into thereaction zone; and, recovering the sixth fraction.

A particular embodiment of the present invention may be characterized bythis separation process wherein the reaction zone comprises analkylation reaction zone, the first component comprises an unreactivediluent, the second component comprises an alkylatable aromaticcompound, and the third component comprises an alkylated aromaticcompound.

A further particular embodiment of the present invention may becharacterized by this separation process wherein the reaction zonecomprises an oligomerization reaction zone, the first componentcomprises an unreactive diluent, the second component comprisespartiallyoligomerized product, and the third component comprisesoligomerized product.

In a more specific embodiment of the inventive process as defined in thethree broad embodiments above, the partial condensing zone contains heatexchanger means wherein at least a portion of the fifth fraction isintroduced as cooling medium before passing into the reaction zone.

These and other more specific embodiments will be more clearly set forthhereinafter.

Many aromatic compounds are utilizable as alkylatable aromatic compoundswithin the process of this invention. The preferred aromatic compoundsare aromatic hydrocarbons, including monocyclic aromatics, polycyclicaromatics, and alkylaromatics, but substituted aromatic hydrocarbons areequally suitable. Such aromatic compounds as phenol, cresol, andhydroxyanisole are among the substituted aromatic hydrocarbons which maybe alkylated to produce an effluent for separation within the scope ofthe inventive process.

Of the alkylatable aromatic compounds suitable for use within theprocess of this invention the monocyclic aromatic hydrocarbons arepreferred and benzene is particularly preferred.

The olefin-acting compound or alkylating agent which may be processedwithin a reaction zone to yield an effluent suitable for separationwithin the embodiments of the inventive process, may be selected fromthe diverse materials including mono-olefins, diolefins, polyolefins,acetylenic hydrocarbons, alcohols, ethers and esters. Among the esterswhich are utilizable are alkylhalides, alkylsulfates, alkylphosphates,and various esters of carboxylic acids.

The preferred olefin-acting compounds are olefinic hydrocarbons andparticularly preferred are the monoolefins. Mono-olefins which areutilized as olefin-acting compounds in the process of the presentinvention may be either normally gaseous or normally liquid at ambienttemperature and include ethylene, propylene, l-butenes, 2-butenes,isobutylene, and higher molecular weight normally liquid olefins.

Also included within the scope of the olefin-acting alkylating agent orolefin-acting compound are certain substances capable of producingolefinic hydrocarbons or intermediates thereof under the conditions ofoperation utilized within an alkylation raction zone or anoligomerization reaction zone. Typical olefin producing substances orolefin-acting compounds capable of use include alkylhalides capable ofundergoing dehydrohalogenation to form olefinic hydrocarbons, andalcohols capable of undergoing dehydration to produce olefinichydrocarbons.

The alkylation of the alkylatable aromatic compound with theolefin-acting compound or alkylating agent will normally be undertakenin the reaction zone in the presence of an alkylation catalyst undersuitable operating conditions. The operating conditions of temperature,pressure and reaction time will vary depending upon the composition ofthe catalyst and the type of olefin-acting compound and alkylatablearomatic compound being processed. Typical operating conditions will beset forth hereinafter. The acid-acting catalyst may be selected fromvarious materials such as sulfuric acid, phosphoric acid, hydrogenfluoride, aluminum chloride, aluminum bromide, boron trifluoride, ferricchloride, zinc chloride, zirconium chloride, various syntheticallyprepared cracking catalysts, such as silica-alumina,silica-alumina-zirconia, silica-magnesia, and various acid-acting claysincluding activated alumina. A particularly preferred catalyst which isutilized for the alkylation of aromatics within the practice of thisinvention is solid phosphoric acid catalyst which is a calcinedcomposite of phosphoric acid and a siliceous absorbent. Anotherpreferred catalyst utilized for alkylation of aromatics within theinventive proces comprising a complex of boron trifluoride with alumina.A further preferred catalyst comprises a composite of silia-alurnina.

The oligomerization of olefin-acting compounds is also undertaken in thereaction zone in the presence of an acid-acting catalyst. Suitableoperating conditions of temperature, pressure, and residence time willvary depending upon the specific catalyst being used and the type ofolefin-acting compound being reacted as will be set forth hereinafter.The acidic catalysts which have been defined hereinabove for thealkylation of aromatic compounds with olefin-acting compounds areequally effective for the oligomerization of olefin-acting compounds. Aparticularly preferred catalyst which is utilized for theoligomerization of olefin-acting compounds within the practice of thisinvention is solid phosphoric acid catalyst which is a calcinedcomposite of phosphoric acid and a siliceous absorbent.

An understanding of the present invention may now be readily obtained byreferring to the accompanying drawing which sets forth a simplified flowfor carrying out one specific example wherein the process of the presentinvention is practiced.

Drawing and example As previously noted, the particularly preferredembodiment of this invention comprises the inventive process wherein thealkylatable aromatic compound is benzene, the olefin-acting alkylatingagent is propylene, the unreactive vapor diluent is propane, and thedesired monoalkylated aromatic compound is high purity cumene. Referringnow to the drawing, a propylene-propane feed mixture enters the processvia line 1 at the rate of 1676.3 moles per hour, at a pressure of about640 p.s.i.g. and a temperature of about 170 F. This propylene-propanefeed contains 48.8 mole percent propylene and is augmented by a propanerecycle stream entering line 1 via line 2 at the rate of 943.6 moles perhour and at a temperature of F. from a source to be specifiedhereinafter. This total combined propylene-propane stream continues inline 1 and is further augmented by a benzene recycle stream which entersline 1 via line 3, from a source also to be specified hereinafter, atthe rate of 6704.7 moles per hour and at a temperature of 290 F. Theresulting combined feed stream then passes via line 1 at 260 F. into analkylation reaction zone which is not shown. The combined feed of 9324.6moles per hour enters the reactor system at 640 p.s.i.g. and ispreheated therein to 380 F. before contacting solid phosphoric acidcatalyst.

A resulting alkylation effluent leaves the reaction zone and enters theinventive process via line 4 at a pressure of about 525 p.s.i.g. and atemperature of about 435 F. This stream comprising 8505.4 moles per houris introduced into a flash chamber 5 at 250 p.s.i.g. and 385 F. Thisalkylation effluent is separated therein into vapor and liquid phases. Apart of the liquid phase is removed from the flash chamber via line 7and comprises a phosphoric acid solution which is leached off of thecatalyst in the reaction zone. This stream normally comprises about onegallon of concentrated phosphoric acid per day and is sent to a disposalsystem not shown. The major portion of the flash liquid comprising4051.1 moles per hour of benzene, cumene, and heavier alkylbenzene,leaves the chamber 5 via line 8 and is sent to fractionation which willbe specified hereinafter.

The flash vapor comprising propane, benzene, and a small quantity ofcumene, leaves the chamber 5 at 250 p.s.i.g. and 385 F. at a rate of 4454.3 moles per hour via line 6 and passes through a heat exchanger 9wherein the vapor is partially condensed by a cooling medium to bespecified hereinbelow. The resulting condensate and vapor passes intoseparator 11 via line 10 at 235 p.s.i.g. and 325 F. The resulting vaporleaves the condensate separator 11 via line 12 and comprises 943.6 molesper hour. This benzene-containing vapor stream comprising propane entersa condenser 15 at 235 p.s.i.g. and 325 F. wherein it is condensed to theliquid phase by a cooling medium to be specified hereinafter. Thecondensed liquid propane is passed via line 16 into receiver 17 :at 225p.s.i.g. and 165 F. The liquid propane which has been collected inreceiver 17 is removed by a pump, not shown, and sent to line 1 via line2 at 640 p.s.i.g. as the propane recycle stream disclosed above.

Fresh make-up benzene which is required for the alkylation process isintroduced into the cumene process unit via line 13 and enters theseparator 11 at 235 p.s.i.g. and 270 F. This fresh benzene is introducedinto the process at this point at the rate of 812.2 moles per hour inorder that it may mix with the partially condensed liquid and pass vialine 14 to the depropanizer column 18 for removal of any trace waterwhich may be in the fresh benzene. The trace water is detrimental toproper catalyst hydration control in the alkylation reactor, and it isthe art to provide for drying of the fresh benzene feed in thedepropanizer column.

A resulting total depropanizer feed of 4322.9 moles per hour leavesseparator 11 via line 14 and enters the depropanizer column 18 at 235p.s.i.g. and 322 F. The

depropanizer column sends a propane vapor overhead via line 19 at therate of 3193.4 moles per hour and at the pressure of 230 p.s.i.g. into acondenser 20 at 120 F. The propane vapor is condensed therein and cooledto 100 F. before passing via line 21 into receiver 22. Reflux for thedepropanizer column is sent from separator 22 into the top of column 18via line 24 at the rate of 2338.0 moles per hour. A net propane overheadproduct leaves separator 22 via line 23 at the rate of 855.4 moles perhour. This net propane product is equivalent to the unreactiveconstituents which enter the inventive process in the propylene-propanefeed at line 1, and is sent to LPG Product Storage or to a fuel gassystem.

A net depropanizer bottoms stream comprising benzene and cumene leavesthe bottom of column 18 via line 25 at the rate of 3467.5 moles per hourat a pressure of 235 p.s.i.g. and a temperature of 425 F. This streamenters line 8 where it is mixed with the hot flash liquid which leavesflash chamber at a rate of 4051.1 moles per hour, as noted hereinabove.The flash liquid in line 8 is at a pressure of 230 p.s.i.g., and atemperature of 385 F., and mixes with the depropanizer bottoms stream toyield a total hot liquid stream which continues in line '8 at the rateof 7518.6 moles per hour. This hot liquid passes into a benzene column26 at a pressure of 20 p.s.i.g. and a temperature of 250 F.

A benzene vapor overhead stream leaves the top of the benzenefractionator via line 27 at p.s.i.g. and 230 F. This vapor stream of9927.7 moles per hour enters condenser 28 wherein it is condensed andcooled to 100 F. The liquid benzene then enters receiver 30 via line 29.A benzene reflux stream is returned to the benzene tower via line 32 atthe rate of 3190.0 moles per hour. A net benzene product is removed fromreceiver 30 via line 31 and sent to storage at the rate of 33.0 molesper hour. This net benzene product comprises benzene and nonaromaticcontaminants which have entered the process as trace non-aromatics inthe fresh benzene feed or in the propylene-propone feed. A total recyclebenzene stream also leaves separator 30 and passes via line 33 at therate of 6704.7 moles per hour into condenser 15.

This recycle benzene stream which enters condenser 15 at 100 F. providesthe specified cooling medium for condensing the propane vapor. Thebenzene recycle leaves condenser 15 at 160 F. via line 34 and enterspartial condenser 9, wherein it provides the specified cooling mediumfor partially condensing the flash vapor. The recycle benzene thenleaves partial condenser 9 at 290 F. and passes into line 1 via line 3as the recycle benzene stream specified previously.

A benzene column bottoms stream comprising cumene and heavieralkylbenzene leaves the benzene column via line 35 at 780.9 moles perhour and at 375 F. This stream passes into a cumene column, not shown,wherein the benzene column bottoms is fractionated to provide 744.4moles per hour of high purity cumene product and 36.5 moles per hour ofheavy alkylbenzene by-product.

Several important advantages of the inventive process may be readilyascertained from the foregoing process description.

The first advantage which will be readily seen is that the depropanizercolumn of the inventive process is reduced in size by about fiftypercent. Whereas the total reactor eflluent of 8505.4 moles per hourwould be charged to the column under the prior art, in the presentinvention only 4322.9 moles per hour is fed to the column. More thanhalf of the benzene, cumene, and polyalkylbenzene of the eflluentby-passes the column as the flash liquid. In addition, none of thepropane recycle passes through the column on its return to the reactionzone. The column diameter may be significantly reduced due to thisreduced loading, and the overhead condensing system and the reboilersystem are accordingly reduced in size. The net result is that thepresent invention yields a considerable savings in the capital cost ofthe depropanizer fractionator.

There is also a reduction of operating cost for the cumene plant due tothe reduction of utilities which are required at the depropanizercolumn. Since more than half of the benzene and cumene bypasses thecolumn, the sensible heat required to elevate the flash liquid to thereboiler temperature is saved. In addition, there is a considerablesaving of heat input at the depropanizer because the recycle propanedoes not pass through the column. If the propane recycle passed into thecolumn, a considerable addition of reflux would be required in order tomake high purity propane recycle. The propane product which leaves thecolumn via line 23 must be benzene-free for use as fuel gas or LPG. Thepropane recycle may be allowed to contain considerable amounts ofbenzene, however, since it is also necessary to recycle benzene to thealkylation reactor. If the propane recycle is passed through thedepropanizer it is forced to meet the purity specification of theproduct propane, thus adding reflux and utilities expense with nobeneficial result to the process. The present invention eliminates thiswasteful utility cost.

There is an additional savings in operating cost in the inventiveprocess. The recycle benzene which must be returned to the reaction zonemust be heated to reaction temperature. A part of this heating isaccomplished by passing the cold benzene through condenser 15 andthrough partial condenser 9. Not only is the benzene heated to 290 F. bythis system, but it provides the cooling medium for these exchangers andthus reduces cooling water requirements for the cumene plant.

Similarly it will be seen that in the particular embodiment describedabove, the recycle propane stream is returned to the reaction zone inadmixture with the propylene and benzene in the combined feed stream.The recycle propane must therefore be preheated to reaction temperatureand if the recycle propane were derived from the depropanizer column therecycle propane would require temperature elevation from F. By thepractice of the present invention, however, the propane recycle requirestemperature elevation from F., thus resulting in a reduction of utilityexpense.

Other advantages in addition to those set forth hereinabove will beapparent to those skilled in the art.

While the embodiment set forth has been specific to the manufacture ofcumene by the inventive process, it must be realized that the presentinvention is also applicable to the manufacture of other alkylatedaromatic hydrocarbons such as ethylbenzene. The inventive process mayalso be found to be eifective in the separation of the eflluent from thesynthesis of other alkylated aromatic compounds, such as alkylphenols,in the presence of an unreactive vapor diluent.

It is to be noted that the operating condition as set forth in theexample are specific to that example and are no way to be construed aslimiting upon the process.

In the alkylation of aromatic compounds with an olefinacting compound itis the art to provide a molar deficiency of the olefin. The molardeficiency of olefin-acting compound to alkylatable aromatic ismaintained by holding an aromatic to olefin molar ratio in the range offrom 2:1 to about 30:1 with a preferred range of 4:1 to about 16:1. Thismolar deficiency is required in order to minimize polyalkylation of thearomatic compound. When utilizing a solid phosphoric acid catalyst inthe reaction zone, it is particularly prefer-red that the ratio ofaromatic to olefin should be about 8:1 when producing cumene and about12:1 when producing ethylbenzene.

The amount of unreactive vapor diluent, propane in cumene synthesis andethane in ethylbenzene synthesis, which is recycled to the reaction zonewill vary as required to maintain the cataly temperature at the desiredlevel. The temperature of the reaction zone may be from 300 F. to about600 F., and when utilizing a solid phosphoric acid catalyst willnormally range from 350 F. to

450 F. for cumene and 450 F. to 550 F. for ethylbenzene. The pressure ofthe alkylation reaction may be from 300 pounds per square inch to 1000pounds per square inch or even higher. The liquid hourly space velocityof the total combined feed to the reaction zone may range from 0.5 to5.0, but will normally be in the range of 1.0 to 1.5. The specificreactor operating conditions which are required for the alkylation ofany aromatic hydrocarbon or other alkylatable aromatic compound whenutilizing a solid phosphoric acid catalyst or any other catalyst arereadily ascertainable by those skilled in the art.

It must be noted that the flash zone was maintained at 385 F. and 250p.s.i.g. in the example given, but that these conditions are specific tothe example. The conditions of temperature and pressure are adjusted togive the desired separation between liquid and vapor in the eflluent.Preferably, these conditions will provide that about half of the benzenein the reactor eflluent will flash into the vapor phase and half willremain in the liquid phase. However, the liquid-vapor split may beshifted up or down as desired by choice of the operating conditions,provided that substantially all of the unreactive vapor diluent is inthe vapor phase. Thus, it is within the scope of the process of thepresent invention that the flash vapor will contain substantially all ofthe unreactive vapor diluent (propane) and that it may contain fromabout 10% to about 90% of the unreacted benzene while the flash liquidmay correspondingly contain from about 90% to about 10% of the benzene.

The primary control of the separation of the eflluent into liquid andvapor is the amount of pressure drop to which the eflluent is subjectedupon leaving the reaction zone and entering the flash zone. As notedabove, it is preferable that the pressure drop, or flashing, shouldprovide that about half of the benzene is in the vapor phase and half isin the liquid phase. Although the alkylation reaction may occur atpressures in excess of 1000 p.s.i.g., little or no flashing of vaporwould occur at such pressure in the flash zone and since the cost offabricating the vessel for the flash zone would be excessive at such apressure level it is advantageous to keep the pressure at about 500p.s.i.g. or below. Since the vapor leaving the flash zone must enter apartial condensing system in order to provide a liquid feed for thesubsequent fractionating column operating under elevated pressure, adepropanizer for cumene synthesis, or a deethanizer for ethylbenzenesynthesis, it is important not to operate the flash zone at a pressurewhich is below the pressure of the subsequent column. Thus, while theflash zone 5 could be maintained at a pressure in the range of fromabout 50 p.s.i.g. to 200 p.s.i.g. this would require that the flashvapor be partially condensed and that the condensate then be pumped intothe fractionating column. It must also be noted that if flash zone 5were operated at such a low pressure level, additional pumping powerwould be required to pump the liquefied propane out of receiver 17 andback to the reactor. Therefore, the pressure within the flash zoneshould be maintained in the range of from 200 p.s.i.g. to about 500p.s.i.g., and it is preferable that the pressure only be suflicientlyhigh to transfer the condensed liquid via line 14 into the subsequentcolumn 18 without mechanical assistance. Thus, it is preferable that theflash zone be maintained at a pressure of from about 200 p.s.i.g. to 500p.s.i.g., and more specifically that the pressure he maintained at from200 p.s.i.g. to about 300 p.s.ig. when applied to cumene production.

The temperature within the flash zone will be the flash point of thereactor eflluent for the specific reactor eflluent composition and forthe specific pressure within the flash zone. The temperature will alwaysbe below the reactor outlet temperature since the flashing of theeflluent will cause a substantially adiabatic temperature drop. Thetemperature Within the flash zone will, therefore, normally be in therange of from about 250 F. to about 500 F., and will preferably be inthe range of from 300 F. to about 425 F. for cumene production.

The degree of cooling which is imposed upon the flash vapor in thepartial condenser 9 will be varied as required to provide the desiredseparation between the propane vapor which is subsequently condensed forrecycle to the reactor, and the net liquid which is charged to thedepropanizer column. In the specific embodiment of the example, theflash vapor was cooled from 385 F. to 325 F. to yield a net propanevapor of 943.6 moles per hour and a net condensed depropanizer liquidfeed of 3510.7 moles per hour. If additional propane recycle weredesired, a part of the recycle benzene cooling medium which enters thepartial condenser 9 via line 34 could by-pass this exchanger, thusincreasing the temperature and providing more propane and benzene in thevapor phase. Similarly, if additional cooling is provided at exchanger 9the temperature will be lowered sufliciently to provide less propane andbenzene vapor for subsequent return to the reaction zone as propanerecycle. The temperature level within the partial condensing zone willbe controlled, typically, between 250 F. and 500 F. and will preferablybe in the range of from 300 F. to 425 F. The pressure level within thepartial condensing zone will be controlled within the limits prescribedhereinabove for the flash zone, since the processing problems discussedtherein apply with equal force to the partial condensing zone.

It should be noted that the foregoing discussion concerning theoperating conditions required within the flash zone and partialcondensing zone are particularly applicable to the separation of aneffluent wherein the sub sequent fractionation columns are operated atsuperatmospheric and atmospheric pressures. It is well known, however,that in alkylating substituted aromatic compounds it is often necessaryto fractionate the eflluent in a train of columns maintained atsubatmospheric pressure. A typical example of such subatmosphericseparation is found in the production of butylated hydroxyanisole fromthe eflluent which results in alkylating p-hydroxyanisole with tertiarybutyl alcohol. When the flash zone and partial condensing zone preceedthe subatmospheric fractionation train, they may be maintained atsuperatmospheric or subatmospheric pressure as may be required toaccomplish the particular degree of separation which may be desired.

The specific operating conditions within the flash zone and partialcondensing zone for any given reactor efliuent composition are readilyascertainable by those skilled in the art utilizing the teachings whichhave been presented hereinabove.

It is to be noted that the fractionation section of the examplecomprises a depropanizer column and a benzene column. The operatingconditions within these fractionation columns are specific for theprocess set forth in the example, and the operating conditions which maybe necessary for any other reactor effluent composition will be readilyascertainable by those skilled in the art. It is not therefore necessarywithin the description of this invention to discuss broad ranges whichare required for such fractionation columns or for the cumene columnwhich is required in the overall process but which was not shown in thedrawing.

It must also be noted that in the example set forth, a solid phosphoricacid catalyst was used in reaction zone for alkylation of the aromatic.Since aromatic hydrocarbons leach water and phosphoric acid from suchcatalyst, provision must therefore be made for removal of concentratedphosphoric acid as indicated via line 7. Where other catalyst systemsare used in the inventive process such provision for acid removal fromthe flash chamber and from the process may not be necessary.

It will be readily seen that the inventive separation process as setforth in the drawing and example above, wherein cumene is recovered froman aromatic-alkylation reactor eflluent, is equally applicable to theseparation of an efiluent from an oligomerization reactor as, forexample, in the recovery of propylene-trimer, propylenetetramer, orheptene fractions. Those skilled in the art will perceive thatpartially-oligomerized product will be returned to the reaction zone vialine 33 for further reaction with olefin to produce the desired fullyoligomerized product in the reaction zone, while the unreactive diluentis returned via line 2 to provide the desired thermal quench in thereaction zone. The benfits which accrue to the cumene process byutilization of the inventive separation process are, therefore, equallyrealized when applying the present invention to the synthesis ofcommercial heptene fractions, propylene-trimer, and propylene-tetramer.

The reactor conditions which are required for the synthesis of hepteneand of propylene-trirner and tetramer fractions are well known in theart and it is not necessary to detail them herein. The conditions whichare indicated hereinabove for the alkylation of aromatic hydrocarbons inthe presence of solid phosphoric acid catalyst are generally applicableto the oligomerization of olefins, with the exception that thetemperature in the reaction zone may be held at a higher level.

Since the reactor effluent composition will be dependent upon the ratioof olefin to paraffinic diluent in the reactor feed and the degree ofoligomerization in the reactor, as effected by the specific operatingconditions in the reaction zone, it is not possible to set forthspecific operating conditions for a flash zone and partial condensingzone as applied to an oligomerization process. The necessary conditions,however, are readily ascertainable by those skilled in the art bydiscriminately utilizing the teachings which have been presentedhereinabove in reference to the operating conditions which areutilizable and which are preferable in the synthesis of cumene.

Preferred embodiments From the foregoing it may be summarized that apreferred embodiment of the present invention is a process for therecovery of cumene which comprises passing a total alkylation eflluentcomprising propane, benzene, and cumene, from an alkylation reactionzone into a flash zone maintained at a pressure in the range of from 200p.s.i.g. to 300 p.s.i.g. and a temperature in the range of from 300 F.to 425 F.; withdrawing from the flash zone a first fraction of vaporcomprising propane and benzene, and a second fraction of liquidcomprising benzene and cumene passing the first fraction into a partialcondensing zone maintained at a pressure in the range of from 200p.s.i.g. to 300 p.s.i.g. and at a temperature in the range of from 300F. to 425 F.; withdrawing from the partial condensing zone a thirdfraction comprising propane vapor and a fourth fraction comprisingbenzene liquid; passing the second fraction and the fourth fraction intoa fractionation zone under conditions sufficient to provide at least afifth fraction comprising benzene and a sixth fraction comprising cumenein high concen tration; passing the third fraction and at least a partof the fifth fraction into the reaction zone; and recovering he sixthfraction.

It may be further noted that a particularly preferred embodiment of thepresent invention comprises the embodiment disclosed in the paragraphimmediately above, wherein the partial condensing zone contains heat exchanger means wherein at least a portion of said part of the fifthfraction is introduced as cooling medium before passing into thereaction zone.

The invention claimed:

1. Process for separating a reaction zone effluent containing at leastthree components which comprises the steps of:

(a) passing said effluent from a reaction zone into a flash zonemaintained under separation conditions;

(b) withdrawing from said flash zone a first fraction comprising a firstcomponent and a first part of a second component, and a second fractioncomprising a second part of said second component and a third component;

(c) passing said first fraction into a partial condensing zonemaintained under separation conditions;

(d) withdrawing from said partial condensing zone a third fractioncomprising said first component and a fourth fraction comprising saidsecond component;

(e) passing said second fraction and said fourth fraction into aseparation zone under conditions sufficient to provide at least a fifthfraction comprising said second component and a sixth fractioncomprising said third component in high concentration;

(f) passing said third fraction and at least a part of said fifthfraction into said reaction zone; and,

(g) recovering said sixth fraction.

2. Process of claim 1 wherein said partial condensing zone contains heatexchanger means wherein at least a portion of said part of the fifthfraction is introduced as cooling medium before passing into saidreaction zone.

3. Process of claim 2 wherein said cooling medium condenses said thirdfraction and partially condenses said first fraction.

4. Process of claim 1 wherein said reaction zone comprises an alkylationreaction zone, said first component comprises an unreactive diluent,said second component comprises an alkylatable aromatic compound, andsaid third component comprises an alkylated aromatic compound.

5. Process of claim 1 wherein said reaction zone comprises anoligomerization reaction zone, said first component comprises anunreactive diluent, said second component comprisespartially-oligomerized product, and said third component comprisesoligomerized product.

6. Process of claim '5 wherein said unreactive diluent comprises propaneand said oligomerized product comprises propylene-trimer.

7. Process of claim 5 wherein said unreactive diluent comprises propaneand said oligomerized product comprises propylene-tetramer.

8. Process of claim 5 wherein said unreactive diluent comprises one ofthe group consisting of propane, butane, and a propane-butane mixture,and said oligomerized product comprises heptene.

9. Process for recovery of alkylated aromatic compounds which comprises:

(a) passing a total alkylation eflluent, comprising unreactive diluent,alkylatable aromatic compound, and alkylated aromatic compound, from analkylation reaction zone into a flash zone maintained at a pressure inthe range of from about 200 p.s.i.g. to about 500 p.s.i.g. and at atemperature in the range of from about 250 F. to about 500 F;

(b) withdrawing from said flash zone a first fraction comprising saiddiluent and alkylatable aromatic compound and a second fractioncomprising alkylatable aromatic compound and alkylated aromaticcompound;

(0) passing said first fraction into a partial condensing zonemaintained at a pressure in the range of from about 200 p.s.i.g. toabout 500 p.s.i.g. and at a temperature in the range from about 250 F.to about 500 F;

(d) withdrawing from said partial condensing zone a third fractioncomprising said diluent and a fourth fraction comprising alkylatablearomatic compound;

(e) passing said second fraction and said fourth fraction into aseparation zone under conditions sufficient to provide at least a fifthfraction comprising alkylatable aromatic compound and a sixth fractioncomprising alkylated aromatic compound in high concentration;

(f) passing said third fraction and at least a part of said fifthfraction into said reaction zone; and,

(g) recovering said sixth fraction.

10. Process of claim 9 wherein said alkylatable aro matic compoundcomprises benzene, said unreactive diluent comprises ethane, and saidalkylated aromatic compound comprises ethylbenzene.

14 References Cited UNITED STATES PATENTS 3,364,139 1/1968 Kunesh et al208-364 X 3,368,966 2/1968 Borst et a1 260-683.62 X 3,370,003 2/1968Borst 260683.62 X 3,371,029 2/1968 Weiland 20836l X DELBERT E. GANTZ,Primary Examiner.

C. R. DAVIS, Assistant Examiner.

U.S. Cl. X.R.

